Bhabha's contribution is to have described colonial power as something less secure than either its administrators or its critics had assumed.
Where Said's Orientalism presented a discourse operating with formidable coherence, Bhabha argued that colonial authority is internally divided and perpetually anxious. His key term is mimicry: colonial rule requires the colonized to become recognizable to it — educated, Anglicized, administratively useful — but cannot allow them to become equivalent, since the difference is what justifies the rule. The result is a subject who is "almost the same, but not quite", and that gap is not a failure of the system but a permanent feature of it, producing a resemblance that mocks even when it does not intend to.
From this follow the other terms associated with him. Hybridity names the condition of a colonial encounter in which neither party emerges intact, against nationalist and imperialist accounts that both assume a pure culture prior to contact. The third space is the site of enunciation in which meanings are negotiated rather than transmitted, so that cultures are always translations rather than essences. Ambivalence names the mixture of desire and derision in the colonial relation, which he takes from psychoanalysis rather than from political economy.
The political attraction of the position is that it locates resistance inside the operation of power rather than outside it, so that subversion does not require a pure standpoint. The standing objection, pressed hardest by critics on the materialist left, is that it makes resistance a property of texts and identities and says little about land, labor or the state — and that its prose style, which is genuinely forbidding, insulates it from the objection.